Abstract: mis paper discusses the upper permian natural gas which is absent of comnum geochemical indicators of coal gas in the southern part of Sichuan Basin,but with In-situ gas slmUar to coal gas (Type m)was mixed with the gas (Type U) generated from Chang Xin formation reservoir. So present natural gas of P21 does not have characteristics of coal gas due to undergoing evolution and remaking in high maturity period. In fact.it mainly generated under coal formation geologic and geochemical condition. These are the features of natural gas of tidal construction with coal, condition for oil geneiated and preserved in carbonate rock and high heat evolution. Depending on these features, areas favourable for gas generation and accumulation arc suggested.

Key words: Sichuan Basin, tidal construction, coal gas, geochemical indicator, contributton factor analysis